The present disclosure relates to a recording device and a method thereof which performs recording with regard to an optical recording medium which has a reference surface, where a position guidance element is formed, and a recording layer, which is formed at a depth position different from the reference surface.
As an optical recording medium which performs recording and reproduction of a signal using the irradiation of light, for example, so-called optical discs such as a CD (Compact Disc), a DVD (Digital Versatile Disc), and a BD (Blu-ray Disc: registered trademark) are in wide-spread use.
In the present state of CDs, DVDs and BDs, in relation to the optical recording media which are to be the next generation of optical recording media in wide-spread use, the present applicants have previously proposed a so-called bulk recording type (also simply referred to as bulk type) of optical recording media such as that disclosed in Japanese Unexamined Patent Application Publication No. 2008-135144 and Japanese Unexamined Patent Application Publication No. 2008-179902.
Here, bulk recording is a technique where a large recording capacity is achieved by changing a sequential focus position, performing laser light irradiation, and performing multi-layer recording in a bulk layer 102 in regard to, for example, an optical recording medium (a bulk recording medium 100) which has at least a cover layer 101 and a bulk layer (recording layer) 102 as shown in FIG. 23.
In relation to bulk recording such as this, in Japanese Unexamined Patent Application Publication No. 2008-135144, a recording technique is disclosed which is called a so-called micro-hologram format. In the micro-hologram format, a so-called hologram recording material is used as the recording material of the bulk layer 102. As the hologram recording material, for example, light-cured photopolymer and the like are widely known.
The micro-hologram format is largely divided into a positive-type micro-hologram format and a negative-type micro-hologram format.
The positive-type micro-hologram format is a method where a detailed hologram is formed by two opposing light beams (light beam A and light beam B) focusing on the same position and this becomes a recording mark.
In addition, the negative-type micro-hologram format is a method where a hologram formed in advance is removed using laser light irradiation and the removed portion is a recording mark and is a concept which is the opposite of the positive-type micro-hologram format. In the negative-type micro-hologram format, as an initialization process, a process where holograms are formed in advance in the bulk layer is necessary.
In addition, as a method of bulk recording which is different from the micro-hologram format, the present applicants also proposed a recording method where a void (blank or hole) is formed as a recording mark such as that disclosed in Japanese Unexamined Patent Application Publication No. 2008-179902.
The void recording method is a method where a blank is recorded in the bulk layer 102 described above by laser light irradiation being performed at a comparatively high power with regard to the bulk layer 102 which is configured, for example, by a recording material such as a light-cured photopolymer. As is described in Japanese Unexamined Patent Application Publication No. 2008-179902, the blank portion formed in this manner is a portion with a different refractive index than another portion in the bulk layer 102 and the reflectivity of light is increased at the boundary portion of these portions. Accordingly, the blank portion described above functions as a recording mark and information recording is realized using the forming of the blank marks in this manner.
In such a void recording method, it is possible for it to be sufficient that light irradiation is performed from one side in the recording since holograms are not formed. That is, it is possible that it is not necessary to form a recording mark by focusing two light beams on the same position as in the case of the positive-type micro-hologram format described above.
In addition, in the comparison with a negative-type micro-hologram format, there is a merit that it is possible that an initialization process is not necessary.
Here, in Japanese Unexamined Patent Application Publication No. 2008-179902, an example is shown where irradiation of precuring light is performed before recording in the performing of void recording, but void recording, where the irradiation of precuring light is omitted, is possible.
However, there are bulk recording types (also simply referred to as bulk types) of optical recording media where various types of recording methods are proposed such as that described above, but the recording layer (bulk layer) of the bulk type of optical recording media in this manner does not have an explicit multi-layer structure with the meaning of a plurality of position guidance elements and recording films (reflecting films), where the position guidance elements are formed, being formed. That is, in regard to this point, it is possible to omit the manufacturing process of the plurality of recording films (and the position guidance elements) which are necessary in a case of a normal multi-layer disc, and to that extent, it is possible to achieve a reduction in manufacturing cost.
However, with the previous configuration of the bulk recording medium 100 shown in FIG. 23 as it is, it is not possible to perform a focus servo or a tracking servo when recording without out forming marks.
As a result, in regard to the bulk recording medium 100, a reflecting surface as a reference which has a position guidance element is provided as shown in FIG. 24.
Specifically, a guidance groove (position guidance element) using, for example, formation of a pit or groove is formed in a spiral shape or in a concentric shape in the lower surface side of the cover layer 101, and a selective reflecting film 103 is deposited thereon. Then, with regard to the lower surface side of the cover layer 102 where the selective reflecting film 103 is deposited in this manner, the bulk layer 102 is laminated via, for example, an adhesive material such as a UV curing resin as an intermediate layer 104 in the diagram.
Here, recording of absolute position information (address information) such as radial position information, rotation angle information, and the like is performed using the formation of the guidance groove using a pit, a groove, or the like such as that described above. In the description below, a surface (formation surface of the selective reflecting film 103 in this case), where the recording of absolute position information is performed with the guidance groove formed in this manner, is referred to as a “reference surface Ref”.
In addition, with a medium configuration such as that described above, with regard to the bulk recording medium 100, separately to the laser light (also referred to as laser light for recording and reproduction or simply as recording and reproduction light) for recording (and reproduction) of the marks such as those shown in FIG. 25, laser light for servos (also simply referred to as servo light) is irradiated as laser light for position control.
As shown in the diagram, the laser light for recording and reproduction and the laser light for servos are irradiated onto the bulk recording medium 100 via a common object lens.
At this time, assuming that the laser light for servos reaches the bulk layer 102, there is a concern that a negative influence may be applied to the mark recording in the bulk layer 102. As a result, in the bulk recording methods in the past, with laser light with a different wavelength range from the laser light for recording and reproduction being used as the laser light for servos, the selective reflecting film 103, which has wavelength selectivity where the laser light for servos is reflected and the laser light for recording and reproduction is transmitted, is provided as the reflective layer formed in the reference surface Ref.
With the assumptions above taken into consideration, an operation when mark recording with regard to the bulk recording medium 100 will be described with reference to FIG. 25.
First, when multi-layer recording is performed with regard to the bulk layer 102 where a guidance groove or a reflective film is not formed, the positioning of a layer position where a mark is recorded is set in advance in the depth direction in the bulk layer 102. In the diagram, a case is shown where a total of five information recording layer positions L of a first information recording layer position L1 to a fifth information recording layer position L5 are set as the layer position (mark formation layer position: also called information recording layer position) where a mark is formed in the bulk layer 102. As shown in the diagram, the first information recording layer position L1 is set as a position which is separated from the selective reflecting film 103 (reference surface Ref) where the guidance groove is formed in a focus direction (depth direction) by an amount of a first offset of-L1. In addition, the second information recording layer position L2, the third information recording layer position L3, the fourth information recording layer position L4, and the fifth information recording layer position L5 are set as positions which are separated from the reference surface Ref respectively by a second offset of-L2, a third offset of-L3, a fourth offset of-L4, and a fifth offset of-L5.
Here, the number of layer positions L is not to be limited to five.
When recording with the marks not being formed, it is not possible to perform a focus servo and a tracking servo with each layer position in the bulk layer 102 as a target based on reflected light of the laser light for recording and reproduction. Accordingly, focus servo control and tracking servo control of the object lens when recording is performed so that the spot position of the laser light for servos tracks the guidance groove in the reference surface Ref based on reflected light of the laser light for servos.
However, it is necessary for the laser light for recording and reproduction described above to reach the bulk layer 102 formed more to a lower layer side than the reference surface Ref in order to perform mark recording. As a result, in an optical system in this case, separately to a focus mechanism of the object lens, a focus mechanism (focus mechanism for recording and reproduction light) is separately provided for independently setting up and adjusting a focus position of the laser light for recording and reproduction.
Specifically, as a focus mechanism such as this, an expander is provided which changes the collimation state (divergence/parallel/convergence) of the laser light for recording and reproduction which is irradiated into the object lens. That is, by changing the collimation state of the laser light for recording and reproduction which is irradiated into the object lens in this manner, it is possible for the focus position of the laser light for recording and reproduction to be adjusted independently from the laser light for servos.
By providing the focus mechanism with regard to the laser light for recording and reproduction in this manner, using the performing of the focus and tracking servo control of the object lens described above based on the reflected light of the laser light for servos from the reference surface Ref, the focus position of the laser light for recording and reproduction is matched with the predetermined information recording layer positions L in the bulk layer 102 and is controlled to be a position which corresponds to the guidance groove formed in the reference surface Ref in a tracking direction.
Here, when reproduction is performed with regard to the bulk recording medium 100 where mark recording has already been performed, there is no necessity for the position of the object lens to be controlled based on the reflected light of the laser light for servos as when recording. That is, when reproducing, it is sufficient if the focus and tracking servo control of the object lens is performed based on the reflected light of the laser light for recording and reproduction with a row of marks formed in the information recording layer positions L which are reproduction targets as a target (also referred to as information recording layer L when reproducing).